Flash lamp



Oct. 28, 1958 R. M. ANDERSON arm. 2,857,752

FLASH LAMP Filed April 7, 1954 m\ V) e,

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BULB \loumacc Inventors: Robert M. Anderson, Paul A. Dell.

John D. Nelson, WW K Their Attorney United States Patent FLASH LAMP Robert M. Anderson, Euclid, Paul A. Dell, Highland Heights, and John D. Nelson, South Euclid, Ohio, assignors to General Electric Company, a corporation of New York Application April 7, 1954, Serial No. 421,510 7 Claims. 01. 67-31 Our invention relates in general to flash lamps of the type comprising a bulb containing a loose filling of a readily combustible material and a combustion-supporting medium, such as an oxygenous gas, which enters into a reaction with the combustible material with the resulting emission of an instantaneous flash of actinic light of high intensity. More particularly, our invention relates to a midget or so-called peanut-sized flash lamp of the above general type.

Small size flash lamps are of great advantage in that they not only aflord the user the maximum convenience in respect to the portability thereof but also permit the use of small size, and therefore less cumbersome, reflec-' tors for redirecting the light from the lamp onto the subject or scene to be photographed. Such small size flash lamps also permit more effective utilization of the total light generated by the lamp through the use of properly designed reflectors, such increased utilization thereby ofisetting to a certain extent the reduction in total light est possible total light output which can be obtained from the lamp within a specified flashing time interval without the danger of explosion of the lamp bulb. For this reason, therefore, it has always been the practice in the design of flash lamps heretofore to maintain the developed temperature, and therefore the developed pressure in the lamp bulb at charge flashing, at a level sufliciently low (through the limitation of the intensity of the reaction by the limitation of the combustible material and the oxygen or other combustion-supporting gas in the bulb) to afford the required degree of safety from explosion on charge flashing. To this end, the amount of combustible material per unit volume of bulb space (i. e., the concentration of combustible material in the bulb) heretofore has been maintained at a figure less than around 1 /2 to 1% mg. per cc. of bulb volume.

Also, flash lamps as heretofore generally made have been of the so-called flange seal type in which a flanged glass stem tube carrying the ignition filament is sealed to the neck of the bulb. The sealing of such flange seal type lamps is customarily performed on a combination sealing and exhaust machine which seals the glass stem into the bulb while the latter is positioned with its neck end down, as a result of which the heat rising from the gas sealing fires and from the heated glass parts acts to heat the bulb proper. The lamp bulb is then immediately filled with oxygen or other combustion-supporting gas through the customary exhaust tube thereof and the latter then tipped-oil? to hermetically seal the bulb. Because of the fact that the gas filling operation is performed shortly after the completion of the sealing-in operation, and before'the bulb has had time to cool, the gas filling in Patented Oct. 28, 1958 the bulb therefore becomes heated immediately upon in troduction into the bulb. As a result, the pressure of the gas in the bulb, after the tipping-off of the bulb and the cooling of the bulb and the filling gas to room temperature, drops to a level considerably lower than the initial filling pressure. Since with the conventional gas filling and tipping-off procedure commonly used in lamp manufacture the initial gas filling pressure must be kept below atmospheric pressure (i. e., approximately 760 mm.) in order to prevent the dilation and blow-out of the glass exhaust tube during the subsequent heating thereof to tip it elf, the maximum possible final gas pressure obtainable in the'bulb, with such conventional lamp manufacturing procedures, after the cooling of the bulb and the gas filling therein to room temperature, amounts to around 650 mm. or so at most. As a practical matter, therefore, the use of the flange seal in flash lamps places a limitation on the amount of oxygen which can be made available in the bulb for the light-producing reaction therein.

It is known, moreover, that when the bulb of a flash lamp is of very small size, for example less than around 15 cc. internal volume, the distance or space for the burning particles of combustible material to travel through before striking the bulb wall is too short to permit the complete combustion of all the burning particles before so striking the bulb wall. As a result, an appreciable percentage of the burning particles become cooled to such an extent by their contact with the relatively cool bulb wall as to prevent their complete combustion and therefore the fullest utilization of the light-producing potential thereof. Accordingly, flash lamps employing such small size bulbs, and provided with flange type seals which place a limitation on the amount of oxygen available for the reaction, do not have a light output per unit volume of bulb space anywhere near as high as thatobtainable with larger size flash lamps.

The combustible material most commonly employed for flash lamps at present consists of a loosely distributed quantity of filamentary material of a type commercially known as shredded foil which is made by cutting or shredding a thin sheet or ribbon of suitable metal foil, of aluminum or aluminum-magnesium alloy for instance, into extremely thin ribbons or strands, as disclosed and claimed in U. S. Patents 2,297,368 and 2,331,230, Rippl et al. Up to the present, it has been customary to employ shredded foil strands having a length of the order of eight inches. The use, however, of strands of such length in an extremely small size lamp bulb, say one having a volume of around 6 cc., increases the difficulty of obtaining good distribution of the shredded foil within the bulb by the automatic (i. e., pneumatic) foil-loading methods which are conventionally used to introduce the shredded foil into the bulb. Poor distribution of the shredded foil in the bulb will, of course, adversely affect the timing of the light flash produced by the lamp as well as decrease the efliciency of the burning of the combustible material, thereby resulting in reduced light output from thelamp.

It is an object of our invention, therefore, to provide a flash lamp of the character referred to and which is of appreciably smaller over-all size than any flash lamp heretofore available and which is capable of providing a light flash of sufficient intensity for effective picture tak centration, than in any previous flash lamp of such type but nevertheless possessing greater safety from explosion on charge flashing.

Still another object of our invention is to provide a lamp of ,the type employing shredded aluminum foilas" the combustible material and havinga materially smaller size than any flash lamp heretofore available yet possessing a light output per milligram of combustible material considerably higher than that heretofore obtainable in any previous comparable type miniature flash lamp of less than 15 cc. bulb volume.

A still further object of our invention is to provide an extremely small size flash lamp of the character referred to which is unprotected by an inside lacquer coating on the lamp bulb but is nevertheless effectively prevented from exploding upon charge flashing by an outside lacquer coating on the bulb which will neither char nor burn under the efiect of the intense heat generated by the lamp upon flashing.

Another object of our invention is to provide an extremely small size flash lamp of the type employing, as the combustible material thereof, finely cut strands of metal foil of a length sufliciently short to assure good distribution of the foil strands within the bulb when loaded thereinto by pneumatic loading methods yet long enough to assure the necessary self support for the strands to maintain themselves in their spacially distributed position throughout the bulb.

According to one aspect of our invention, we have found that by employing a very small size and preferably a generally elliptical-shaped bulb having a volume less than 10 60., and preferably of the order of 6 cc., by utilizing the conventional butt-seal method of sealing the lamp igriition mount into the bulb 'to thereby enable the filling of the bulb with oxygen, by the conventional gas filling and tipping-off methods, to a pressure higher (of the order of at least 700 mm.) than that obtainable with the so-called flange seal method of sealing lamps heretofore generally employed in flash lamp manufacture, and by loading the bulb with a conventional type filamentary combustible material to a concentration greater than any heretofore employed in flash lamps, it is possible to produce'a flash lamp having a materially higher total light output 'per unit volume of bulb space yet a higher degree of safety from explosion than any previously known flash lamp.

A further aspect of our invention is the use, as the combustible filling material for such extremely small size lamps, of finely cut strands or ribbons of thin metal foil having a strand length within the rangeof from approximately 1 to inches whereby to'no't only assure the necessary self-support for the strands to maintain themselves in position distributed throughout-the interior space of the bulb, but to also insure better distribution and more effective ignition of the combustible material and better light production therefrom.

Further objects and advantages of the invention will appear from the following detailed description of a species thereof and from the accompanying drawing in which:

Fig. l is an elevation of a flash lamp comprising our invention;

Fig. 2 is an elevation at right angles to Fig. l and showing the base of the lamp in section;

Fig. 3 is a fragmentary sectional view, on a greatly enlarged scale, of a portion of the wall of the lamp bulb; and

Fig. 4 is a graph illustrating the light production per unit volume of bulb space and per milligram of'combustible material of previous type flash lamps in comparison to that of the lamp of our invention.

Referring to the drawing,'-the flash lamp according'to the invention comprises a small soft glass bulb I preferably generally ellipsoidal in shape and having a small diameter neck portion 2 extending axially of the bulb from one end thereof. In accordance with the invention, the bulb 2 is of a size smaller than that employed in any flash lamp commercially available at present, the bulb having a volume of less than cc. and preferably of the order of 6 cc., and the neck portion having an outside diameter of the order of inch.

Sealed into the neck end of the bulb 1, by a butt-seal such as is conventional in miniature incandescent lamps, is a lamp ignition mount 3 comprising a pair of lead-in wires 4 which, in the manufacture of the lamp, are sealed between the end of the bulb neck 2 and the end of an exhaust tube 5 abutted thereagainst, the exhaust tube 5 being subsequently tipped off, as indicated at 6, to thereby hermetically seal the bulb. The lead-in wires 4 extend into the bulb 2, from the region of their seals thereinto, in a direction approximately longitudinally of the bulb and in more or less parallel relation, and are rigidly tied together and held in place by a supportbead 'Z of glass or other suitable insulating material in which the lead-in wires are embedded. The lead-in wires 4 terminate at their inner ends in the vicinity of the mid-region of the bulb 1, and they are bridged at their said inner ends by an ignition filament 8 preferably consisting of a short straight length of fine tungsten wire having a diameter preferably of the order of 0.7 mil. The inner tips or ends of the lead-in wires 4 are provided with coatings or heads 9 of a suitable fulminating or primer ma terial, which beads are in contact with the filament 8 and become ignited when the latter is energized and heated. If desired, the inner ends of the lead-in wires 4 on which the heads 9 of fulminating material are located may be bent over to extend laterally and lie in a plane transverse to the bulb axis, in accordance with the invention disclosed and claimed in U. S. Patent No. 2,729,960 of R. M. Anderson, filed January 2, 1952, and assigned to the assignee of the present invention. Externally of the bulb 1, the lead-in wires 4 are connected to the end eyelet contact 10 and the side shell contact 11 of a base 12 suitably secured to the neck end 2 of the bulb, as by means of a ring 13 of conventional basing cement.

The fulminating material 9 preferably is of the general type disclosed and claimed in U. S. Patent 2,280,598, G. H. Meredith, issued April 21, 1942, and comprising an admixture of fine (i. e., of the order of 325 mesh or finer) No. 3 grade magnesium, zirconium and potassium perchlorate powders bonded together by a suitable binder such as a 2-5% solution of nitrocellulose in amyl acetate. For best results, however, and particularly where the ignition filament 8 is of a diameter of the order of 0.7 mil, it is preferred that the relative proportions of the above-named powder ingredients be within the particular ranges disclosed and claimed in U. S. Patent No. 2,756,577, .R. M. Anderson, filed of even date herewith and assigned to the assignee .of the present invention, such ranges being of the order of from 6090% zirconium, l8% magnesium, and 9-35% potassium perchlorate.

To strengthen the bulb 1 and render it substantially shatterproof on charge flashing, a protective lacquer coating 14 (Fig. 3) of the type disclosed and claimed in co-pending U. S. Patent .No. 2,291,113, R. M. Anderson, filed of evendate herewith and assigned to the assignee of the present invention, is applied to the outer side of the bulb, the inner side of the bulb being left bare or unprotected by a lacquer coating. As therein disclosed, and as shown in Fig. 3, the outside lacquer coating 14 comprises a double layer coating consisting of two distinct superimposed lacquer films, i. e., a base of buffer coating 15 and an outer coating 16. 'The base or buffer coating 15 consists of a lacquer of good heat-absorptive properties sufficient to insure-therequired amount of absorption of the heat generated within the lamp on charge flashing to prevent the charting and consequent weakening of the outer coating 16. The said outer coating 16 consists of a relatively high tensile strength structurally-reinforcing lacquer material. For the abovestated purposes, the base or buffer coating may comprise a polyvinyl resin such as polyvinyl acetate, polyvinyl acrylate, and polymethacrylates such as ethyl metharerylate, methyl methacrylate, butyl methacrylate, isobutyl methacrylate and copolymers and mixtures of the said polymethacrylates. The polymethacrylates have been found to be particularly suitable for use as the buffer coating 15 however, and of the various polymethacrylates mentioned above it is preferable to employ isobutyl methacrylate. The outside coating 16 may consist of any suitable lacquer material possessing sutficient tensile strength to structurally reinforce the bulb during charge flashing. However, cellulose acetate and cellulose acetate butyrate have have been found to be particularly suitable for this purpose.

The bulb 1 contains a filling of oxygen or other combustion-supporting gas and a quantity of combustible filamentary light-giving material 17 which, on ignition by the filament Sand primer 9 constituting the ignition means of the lamp, enters into a reaction with the filling gas to produce a momentary flash of actinic light of high intensity suitable for picture-taking purposes. The combustible material 17 may consist of aluminum or an aluminum-rnagnesium alloy in filamentary form, such as fine wire of the order of 1.5 mils or less in diameter. Preferably, however, the combustible material 17 is in the form of fine cut strands of thin aluminum foil such as that commercially known as shredded foil and produced by the method and apparatus described and claimed in the aforesaid Rippl et al. Patents 2,297,368 and' 2,331,230, such shredded foil strands having a width of the order of 1 mil or less and a thickness likewise of the order of 1 mil or less. The filamentary material 17 is distributed loosely within the bulb and as uniformly as possible throughout the space occupied thereby in order to insure the most favorable combustion conditions for the said material.

Heretofore, the individual strands of shredded foil customarily employed for the manufacture of flash lamps of the shredded foil type have generally been of a length of the order of 8 inches. While strands of such length are entirely suitable for use in the larger size flash lamps, in the case of bulbs of the size with which the invention is concerned (i. e., bulbs having a volume of less than cc. or thereabouts) we have found that better distribution and better ignition of the shredded foil is obtained by limiting the length of the individual strands of shredded foil to a length of the order of 5 inches or less. Expressed in another Way, the individual strands of shredded foil are preferably limited to a length such that the ratio of their length in inches to the inside perimeter in inches of the bulb in an axial (longitudinal) plane thereof is no greater than approximately 2. The use of such shorter strands of shredded foil has the advantage of affording a great many more loose ends serving as ignition points for a given weight or charge of shredded foil in the lamp bulb, thereby facilitating the ignition of the shredded foil in a manner such as tends to produce increased useful light output therefrom. If the strands of shredded foil are too short, however, they will not maintain themselves in place in the bulb in distributed position therein but instead will drop down or collapse into the bottom region of the bulb. To prevent such collapsing of the shredded foil load in the bulb and assure its proper self-support therein, we have found it necessary to maintain the individual foil strands above a certain minimum length. Thus, for use in the extremely small size flash lamp of our invention, employing bulbs having a volume less than 10 cc., the foil strands should have a length at least of the orderof 1 inch or, in other words, a length such that the ratio of the individual Since the sealing of butt-seal type lamps such as the flash lamp of our invention is customarily performed on a machine which seals the lamp mount 3 into the bulb 1 while the latter is held in an inverted or neck-up position, the heat rising from the gas sealing-in fires and from the heated glass parts of the lamp therefore does not tend to heat the bulb proper to any great extent. More over, with such conventional butt-sealing practice, the introduction of the gas filling into the bulb is not performed immediately after the sealing-in operation but instead is normally performed on a separate machine after the lapse of an appreciable period of .time during which the bulb ordinarily has suflicient opportunity to cool to room temperature. The sumresult of these two factors, therefore, is that the oxygen or other gas filling introduced into the bulb does not become heated and expanded in the bulb, prior to the tipping-off of the latter, such as to subsequently cause any appreciable contraction, and consequent reduction in the pressure of the gas filling in the bulb. Accordingly, the gas filling in such butt-seal type lamps remains approximately at the initial filling pressure thereof. The use of. the butt-seal construction therefore enables the production of flash lamps with final oxygen pressures materially higher than it is possible to obtain, with standard manufacturing procedures, in conventional flange-seal type flash lamps. Thus, it is possible to produce, by the use of conventional manufacturing methods, butt-seal type flash lamps having oxygen filling pressures of the order of 700 mm. of mercury and above. Accordingly, the flash lamp comprise ing our invention is provided with a combustion-supporting gas filling, preferably oxygen, at a pressure at least of the order of 700 mm. of mercury.

As mentioned previously, in the manufacture of flash lamps as made heretofore, the amount of combustible material per unit volume of bulb space has been maintained at a concentration of less than around 1 /2 to 1% mg. per cc. of bulb volume in order to thereby limit the intensity of the reaction in the bulb on charge flashing, and therefore the developed pressure in the bulb, to a level sufliciently low to afford the required degree of safety from explosion. Because of this prior self-imposed limitation on the concentration of combustible material in the bulb for safety considerations, and further because of the failure of all the combustible material in a small size bulb to undergo complete combustion ,together with the limitation on the oxygen pressure which can be provided in the bulb of a flange-seal type lamp by the use of present commercially practicable manufacturing methods, the light output per unit volume of bulb space produced by prior type flash lamps employing small size bulbs of, for example less than 15 cc. volume, has been considerably lower than the light output per unit volume of the most efficient larger size flash lamp in this respect. This is clearly illustrated by curve A in Fig. 4 representing the light output per cc. of bulb volume of various commercial type flash lamps presently available,'the curve clearly indicating that flash lamps of 15 cc. or less bulb volume produce less light output per cc. of bulb volume than flash lamps of around 25 to 30 cc. bulb volume which, prior to our" invention, were the most efficient in this respect. However, We have found that a butt-seal type flash lamp employing a verysmall bulb of less than about 10 cc. volume and filled with oxygen gas at a pressure at least of the order of 700 mm. of mercury and containing a loosely distributed quantity of conventional type filamentary combustible material in a concentration greater than 1% mg. per cc. of bulb volume, will produce a higher light output per unit volume of bulb space (i. e., will be a more prolific generator of light for a given bulb volume),

while at the same time possessing a higher degree Of.

safety from explosion on chargeflashing, than any known previous type flash lamp. Thus, while the highest light output per unit volume of bulb space for any known prior type flash lamp has been .oflthe order of.650.lumen seconds per cc. of bulb volume, the comparable figure for the flash lamp according to our invention'is ofthe order of 710 or more :lumen seconds per cc. of .bulb volume, as denoted by the point P on the chart of Fig. 4, which not only constitutes a material variance from the .curve of Fig. 4 and represents an increase of nearly 15% over the highest light .output percc. of bulb volume of any known prior type miniature iflash lamp having a bulb volume of less than 15 cc. .and of approximately 30% over the light output .per cc. of bulb volume that normally would be expected, by extrapolation of the curve A, from a comparable size (.i. e., 6 cc. bulb volume) flash lamp, but also represents an :increase of nearly 10% over the highestlight output per cc. of bulb volume of any known .prior type .flash lamp regardless of bulb size. Moreover, properly constructed flash lamps according to the invention have shown practically 100% freedom from explosion on charge flashing. Of most importance, however, is the fact that flash lamps according to the invention are practically free .from explosion on charge flashing even though, through faulty construction or subsequent damage, the lamp becomes a so-called leaker or airlamp. This is in marked contrast to previous type flash lamps which, under similar circumstances, would be apt to explodelin most-cases. For such reasons, therefore the flash lampof our invention is the safest from explosion on charge flashing of any flash lamp known.

In addition to producing a higher light output per cc. of bulb volume than any knownprior type flash lamp, the flash lamp of our invention also produces a considerably higher light output per mg. of combustible shredded aluminum foil'than that which would ordinarily be expected from a flashlamp of such bulb size employingsuchtype combustiblematerial. This is readily apparent from the curve B in Fig. 4 representing the light output per mg. of combustible material of various known commercial type flash lamps employing pure aluminum shredded foil as the combustible material. From this curve B it will be seen that the light output per mg. of combustible material ordinarily decreases as the bulb size or volume diminishes, such decrease resulting from the greater difliculty of obtaining complete and effective combustion of all the combustible material in the bulb thesmaller the size thereof. However, a miniature flash lamp of the particular construction comprising our invention, even though having a bulb volume as much as 50% or more smaller than that of other known miniature type flash lamps having a bulb volume of less than cc. and employing pure aluminum shredded foil as the combustible material, will nevertheless produce a higher light output per mg. of combustible material than that produced by such other type flash lamps and therefore constitutes a more eflicient generator of light for a given weight of shredded aluminum foil. Thus, while the light output per mg. of combustible material for any known prior type flash lamp of a bulb volume less than 15 cc. and employing shredded aluminum foil as the combustible material has been of the order of 350-360 lumen second per mg. of combustible material, the comparable figure for the flash lamp of our invention is of the order of 390 or more lumen seconds per mg. of combustible material, as denoted by the point Q on the chart of Fig. 4, which not only constitutes a material variance from the curve of Fig. 4 and represents an increase of the order of 30% over the light output per mg. of combustible material that normally would be expected, by extrapolation of the curve B, from a comparable size (i. e., 6 cc. bulb volume) flash lamp employing shredded aluminum foil, but also represents an increase of nearly 10% even over the light output per mg. of combustible material (of any known prior type ,flash r-lamp {having ,a

bulb volume less than 15 cc. and employing shredded aluminum ;foil as thecombustible material.

.As aspecific example thereof, a flash lamp according to our invention comprises an elliptical-shaped bulb 1 having a volume of approximately 6 cc. and containing oxygen at a pressure of around 700 mm. of mercury. The bulb 1 ;is,filled .with approximately 11 mgs. of shredded aluminum foil 17 distributed loosely within the bulb, the individuallstrands of shredded foil having a length .of approximately 4 .inches, a Width of approximately 0.0008 inch, and a thickness of approximately 0.00055 inch. The primer heads 9 are composed of a fine (i. e., of the ordergof 325 mesh or finer) powder admixture of approximately 7% by weight of magnesium powder, approximately 64% by .weight of so-called No. 3 grade zirconium powder, and approximately 29% by weight of potassium perchloratepowder, bonded together by a 2% solution of nitrocellulose in amyl acetate. The ignition filament 8consists of a short (approximately 60 mil) length of 0.7 mil diameter straight tungsten wire. The inside surface of the bulb 1 is left bare, i. e., is uncoated with any-protective lacquer, while the outside surface is provided with a.double-layer lacquer coating the underlayerorbuflfer coating of which consists of at least 200 mgs. of isobutyl methacrylate and the outer layer of which consists of at least .250 mgs. of cellulose acetate. Flash lamps of the .above specific construction will ,produce .a momentary flash of light of approximately 4250 lumen seconds with a peak intensity of between 550,000 and 600,000 lumens and which, through :the control of the size of the primer beads 9, will have a total duration of less than 25 milliseconds, and will.peak;at approximately 15 milliseconds, following theclosureof the electrical'circuit through the ignition filament 8.0f the lamp. .Such a flash lamp having the above-described flash characteristics is therefore eminently suited as alight source for use with ordinary inexpensive typecameras not ,provided with flash lamp synchronizingmeans and wherein the so-called open-flash" method of taking flash lamp pictures is employed, the flash lamp in such case being flashed during the interval when the camera shutter is in an open position such as occurs when a camerashutter set for time or bulb is actuated. In addition, such a flash lamp is particularly well suited as a light source for use in conjunction with the extremely sensitive (high-speed) photographic films recently introduced on the market, such as that commereially known as Eastman Royal Pan and Du Pont Superior Pan Press, type 446.

Although a preferred .embodiment of our invention has been disclosed, it will be understood that the invention is not to be limited to the specific construction and arrangement of parts shown, but that they may be widely modified within the spirit and scope of our invention as defined by the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A flash lamp comprising a sealed bulb having a volume of less than about 10 cc., a mount sealed into said bulb, a filling of .a combustion-supporting gas in said bulb at a pressure of at least of the order of 700 mm. of mercury, a quantity of combustible metallic filamentary material loosely distributed within said bulb, the quantity of filamentary material in said bulb amounting to at least approximately 1% mgs. per cc. of bulb volume, and ignition means carried by said mount and located in said bulb for igniting said combustible material, said lamp producing a total light output per unit bulb volume of at least 700 lumen seconds per cc.

2. A flash lamp comprising a sealed bulb having a volume of less than about 10 cc., a mount sealed into said bulb by a butt seal, a filling of a combustion-supportin gas at a pressure of at least of the order of 700 mm. of mercury,,a quantityof combustiblemetallic filamentary material loosely distributed within said bulb.

, 9 Said filamentary material comprising a plurality of individual strands having a length of the order of from one to five inches, and ignition means in said bulb for igniting said combustible material, said lamp producing a total light output per unit bulb volume of at least 700 lumen seconds per cc.

3. A flash lamp comprising a sealed glass bulb having a volume of less than about 10 cc., 2. mount sealed into said bulb by a butt seal, a filling of a combustion-supporting gas at a pressure of at least of the order of 700 mm. of mercury, said bulb heaving its interior surface exposed and its exterior surface provided with a suitable lacquer coating, a quantity of combustible metallic filamentary material loosely distributed within said bulb, the quantity of filamentary material in said bulb amounting to at least approximately 1% mgs. per cc. of bulb volume, and ignition means in said bulb for igniting said combustible material, said lamp producing a total light output per unit bulb volume of at least 700 lumen seconds per cc.

4. A bash lamp comprising a sealed bulb having a volume of the order of 6 cc., a mount sealed into said bulb by a butt seal, an oxygen atmosphere at a pressure of at least about 700 mm. of mercury, a quantity of combustible filling material in said bulb comprising a fiufied out mass of fine strands of a metallic material consisting essentially of aluminum, said strands having a length of the order of from one to five inches, the quantity of filamentary material in said bulb amounting to at least approximately 1% mgs. per cc. of bulb volume, and ignition means in said bulb for igniting said combustible material, said lamp producing a total light output per unit bulb volume of at least 700 lumen seconds per cc.

5. A flash lamp comprising a sealed bulb having a volume of the order of 6 cc., a mount sealed into said bulb by a butt seal, an oxygen atmosphere at a pressure of at least about 700 mm. of mercury, a combustible in said bulb comprising of the order of 11 mgs. of fine cut strands of a metallic material consisting essentially of aluminum, said strands having a thickness of the order of 0.00055 inch, a width of the order of 0.00080 inch and a length of the order to form one to five inches and being loosely distributed throughout the interior space of said bulb, and ignition means in said bulb for igniting said com- 10 bustible material, said lamp producing a total light output per unit bulb volume of at least 700 lumen seconds per cc.

6. A flash lamp comprising a sealed bulb having a volume of the order of 6 cc. and having its interior surface bare and its exterior surface provided with a suitable lacquer coating, a mount sealed into said bulb by a butt seal, a filling of oxygen in said bulb at a pressure of at least about 700 mm. of mercury, a combustible in said bulb comprising of the order of 11 mgs. of fine cut strands of a metallic material consisting essentially of aluminum, said strands having a thickness of the order of 0.00055 inch, a width of the order of 0.00080 inch, and a length of the order of from one to five inches and being loosely distributed throughout the interior surface of said bulb, and ignition means carried by said mount and located in said bulb for igniting said combustible material, said lamp producing a total light output per unit bulb volume of at leaet 700 lumen seconds per cc.

7. A flash lamp comprising a sealed bulb having a volume less than 10 cubic centimeters, a mount for ignition means sealed into the wall of said bulb, a filling of a combustion supporting gas in said bulb at a pressure not less than about 700 millimeters of mercury, a mass of combustible filamentary material loosely dispersed in the interior of said bulb, the quantity of filamentary material amounting to not less than about 1% milligrams per cubic centimeter of bulb volume, and ignition means carried by said mount and located in the interior of said bulb for igniting said combustible material, said lamp upon flashing producing a light output of at least 700 lumen seconds per cubic centimeter of bulb volume and at least 390 lumen seconds per milligram of combustible material.

References Cited in the file of this patent UNITED STATES PATENTS 2,046,388 Kurlander July 7, 1936 2,306,563 Pipkin Dec. 29, 1942 2,324,959 Stevens July 20, 1943 2,351,290 Rippl et a1 June 13, 1944 2,359,483 Kuebler Oct. 3, 1944 2,386,672 Fink Oct. 9, 1945 

1. A FLASH LAMP CONSISTING A SEALED BULB HAVING A VOLUME OF LESS THAN ABOUT 1 0 CC., A MOUNT SEALED INTO SAID BULB, A FILLING OF A COMBUSTION-SUPPORTING GAS IN SAID BULB AT A PRESSURE OF AT LEAST OF THE OTHER OF 700 MM. OF MERCURY, A QUANTITY OF COMBUSTIBLE METALLIC FILAMENTARY MATERIAL LOOSELY DISTRIBUTED WITHIN SAID BULB, THE QUANTITY OF FILAMENTARY MATERIAL IN SAID BULB AMOUNYING T AT LEAST APPROXIMATELY 1/34 MGS. PER CC. OF BULB VOLUME, AND IGNITION MEANS CARRIED BY SAID MOUNT AND LOCATED IN SAID BULB FOR IGNITING SAID COMBUSTIBLE MATERIAL, SAID LAMP PRODUCING A TOTAL LIGHT OUTPUT PER UNIT BULB VOLUME OF AT LEAST 700 LUMEN SECONDS PER CC. 